1. Field of the Invention
The present invention relates to a bioactive glass ceramic used in artificial bone and dental implants and a process for the preparation thereof.
2. Description of the Prior Art
Extensive research has been conducted to aid the recovery mechanisms of a patient's body which includes a human body. Research has been especially directed to aiding the repair of bone damaged by disease, injury, aging, congenital disease, and the like with artificial materials. Recently, many materials applicable to living tissue have been developed and used.
These materials which are applied to living tissue are referred to as bioactive, and are directly implanted to living tissue in a patient. Bioactive material, or biomaterial, should have good biocompatibility with the patient. Furthermore, some components released by the biomaterial that respond chemically with the patient's body should be nontoxic. Also, after implanted in the body, the biomaterial should not undergo chemical changes that diminish its strength or convert it into toxic material.
Some materials such as metals and high polymers are used as biomaterial in a living body. There are problems associated with the use of metal as a biomaterial, however. These problems include transformation of the metal surface, the solution of metal ions, and poor biocompatibility. High polymers tend to lack sufficient mechanical strength and biocompatibility. Also, monomers dissolved from such a high polymer material can be toxic.
In addition to metals and high polymers, ceramics have been used as biomaterials. Ceramics have demonstrated the advantage of non-toxicity since the components dissolved from ceramics are nontoxic. In particular, Al.sub.2 O.sub.3 ceramic is not harmful to a patient and has high mechanical strength (1270 MPa of bending strength). Accordingly, Al.sub.2 O.sub.3 has been used as material for artificial bone and artificial dental implants. However, Al.sub.2 O.sub.3 ceramic is inactive within a living body, i.e., not bioactive, and thus, cannot chemically bond with bone. Attachment of such an inactive material to living bone requires mechanical joining, e.g., providing a hole in the inactive material so that new bone grows into the hole, thereby joining the bone and inactive material.
To overcede the problems mentioned above, Bioglass.RTM. (Hench) has been developed. Bioglass.RTM. is a member of the Na.sub.2 O--CaO--SiO.sub.2 --P.sub.2 O.sub.3 group of bioactive glass. Although Bioglass.RTM. has good biocompatibility, it is not generally utilized because its bending strength is too low (72.+-.25 MPa) to be used alone under load-bearing conditions.
To improve the bending strength of Bioglass.RTM., Ceravital.RTM. (Bromer), which is prepared by precipitating the apatite from a glass, and a high density hydroxyapatite (Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2) sintered composite (compressive strength: 509 MPa) have been developed. These compositions are capable of chemically bonding with living bone, but have several defects including insufficient mechanical strength and complicated preparation processes.